Communication apparatus



June 13, 1939- R. H. CAMPBELL 2,162,368

COMMUN ICATION APPARATUS June 13, 1939. R. H. CAMPBELL 2,162,368

COMMUNICATION APPARATUS Filed June 29, 1937 2 Sheets-Sheet 2 Patented June 13, 1939 UNITED STATES PATENT OFFICE 2,162,388 COMMUNICATION APPARATUS Application June 29, 1931, Serial No. 150,951

22 Claims.

This invention relates to communication apparatus, and particularly to telephonie communication apparatus in which suitable voice receiving and transmitting means, such as .dynamic loud speakers of the type comprising a permanent magnet, are employed for the dual function of receiving and transmitting, the iiuctuatlons in electrical current created in the receiver being amplified by a suitable ampliiier.

According to the present invention I provide a dominant or central instrument at a location hereinafter termed a. central station, and one or more secondary instruments located at suitable positions remote therefrom and hereinafter termed remote stations. I provide a switch at the central station and bias it to a normal position conditioning the system for communication from the remote stations to the central station. when it is desired to communicate in the opposite direction, that is from the central station to the remote stations, this switch must be operated to another position and when in that position the remote stations are unable to communicate with the central station. Each of the remote stations is provided with a switch occupying a normal position conditioning the remote station for the reception of speech. When this switch is moved to its other position. the remote station is conditioned from the transmission ot speech from it to the central station, provided, of course, that the aforementioned switch at the central station is in its normal position.

As will be fully understood from the following description o! preferred embodiments o! the invention, the switches effect the connection of the input and output ends4 of the amplifier to the transmitting and receiving loud speaker, respectively.

One of the objects oi the invention is to provide an apparatus of this type in which a central station and a plurality of remote stations is provided, each of said remote stations being adapted for direct conversation with the central Itation without communicating to the other remote stations.

A further object of the invention is to provide communicating apparatus in which the central station may talk and be talked to, by a selected one ofthe plurality of remote stations, each oi' said stations being normally adapted to talk to the central station when desired.

A further object of the invention is to provide communicating apparatus oi' this type in which a central station is normally adapted to talk to all of the plurality of remote stations, each of whlchis adapted to be switched to non-receiving and transmitting condition.

A further object oi the invention is to provide a communicating system oi this type in which a central station is switched to communicate with any one o! a plurality of remote stations so that conversation can be carried on exclusively therebetween, said central station being dominant so that it can be preferentially connected to the input end of the amplifier at the will o! the central operator.

A further object of the present invention is to provide a communicating system oi this type in which any oi the remote stations may cause a regenerative signal at the central station.

Other objects, advantages and capabilities of the invention will appear from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic view oi one embodiment of my invention;

Fig. 2 is a diagrammatic view of a modified embodiment oi my invention; r

Fig. 3 is a diagrammatic view oi a further modiiled embodiment of my invention, and

Fig. 4 is a diagrammatic view of still another' modiiied embodiment oi.' my invention.

Referring first to Fig. l, the reference numeral Il designates voice receiving and transmitting means, such as a dynamic loud speaker unit of the type employing a permanent magnet and a voice coil suspended in the ileld thereof, located at a station from which the communication system is to be controlled. This station may be aptly termed either a master or central station, and hereinafter will be referred to as a central station.

Speaker units Il, similar in all respects to units il. are located at one or more remote stations between which and the control station it is deaired to communicate.

The nuctuations in current produced in the units. when acting as receivers. are ampliiled by an amplifier I2 o! any suitable type comprising one or more stages oi amplication. It may be provided with volume control as well as a switch for connecting it to a suitable source of power, but since these elements, as well as the amplifier itself, may be of any well known construction. l

they are not illustrated or described in great detail herein. For present purposes it is sui!!- cient to state that one terminal oi both the input and output of the amplifier are connected to a common grounded conducor I3 that extends 2 aieasas from the central station to all remote stations. as will appear hereinafter.

A selectively operable switch Il is provided at the central station for connecting the speaker unit Iii thereat to either the output or input of the amplifier, and at the same time either condition the remote speaker units Il for connection to the input of the amplifier by selectively operable switches I5 at the remote stations, or directly connect the remote speaker units to the output of the amplifier. The switch Il is biased by suitable means, such as a spring, to a position in which the speaker unit Ill is connected to the output and the units II are conditioned for connection to the input by switches I5, whereby any of the remote stations may communicate with the central station.

The switch Il is a double pole double throw switch having its iirst switch blade I5 connected by a conductor Il to the output of the ampliiler. and its other switch blade I8 connected by a conductor I9 to the input of the amplifier. The switch is biased into a position in which the blade I6 engages one of a pair of interconnected contacts 20 and the blade I3 engages a contact 2 I. When the switch is operated from its normal position, the switch blade I5 engages a contact 22 and the switch blade I8 engages another of the interconnected contacts 23.

When the switch Il is in its normal position, as illustrated in Fig. 1, the speaker unit IIl is connected to the output of the amplifier by means of a conductor 23 connecting one terminal of the voice coil 2l to the interconnected contacts 20, the other terminal o! the voice coil being connected to the common conductor I3. In its normal position the switch Il also conditions the remote speakers for connection to the input through a conductor 25 leading from contact 2i to the switch I5 of a first remote station and having a plurality of branch conductors 23 and 21 leading to other remote stations. 'I'he switches I 5 are all biased to an open position from which they may be operated to engage contacts 28 connected directly to the voice coils 29 of the remote speaker units. Whenever a switch I5 is operated luto engagement with the contact 23 and the switch I4 is in its normal position, a voice coil 29 is connected directly across the input of the amplier through a circuit including the common conductor I3 and branch conductors I3' leading from the latter to the voice coils or the speaker units at remote stations.

When the switch Il is operated to its displaced position, the speaker unit Ill at the central station is connected to the input` of the amplifier through switch blade il and conductor I9 and the remote speakers are connected directly to the output of the amplier through conductor I1, switch blade I5 and a conductor III leading from contact 22 to the junction of the various contacts 2B with their respective voice coils.

From the above detailed description of the invention, it may be seen that whenever the switch Il at the central station ls in its normal position, any of the remote stations may communicate with the central station upon operation of the switch I5 at the remote station into engagement with the contact 28. Upon the operation oi' switch I5 in this manner, the voice coil associated with the speaker unit at `the remote station is connected across the input ot the ampliiler through the switch, conductor 25, switch blade IB, and conductor I9. The amplified signals are impressed upon the speaker III at the central station through a circuit including the conductor I1, switch I6, and conductor 23 leading to the voice coil 2l.

Aiter the remote station has communicated Y with or called the central station, the operator at the latter station may manipulate switch I4 to its displaced position and communicate with the remote station. At this time the unit I at the central station is connected across the input of the amplifier through conductor I9, switch blade I8, and conductor 23, and the speakers II are connected to the output of the amplifier through conductor il, switch blade I6 and conductor 30. Whenever the switch I4 is operated into its displaced position, the remote stations cannot communicate with the central station because actuation of the switch I into engagement with contact 28 has no effect inasmuch as conductor 25 is not actively associated with the arnplifler in the displaced position of switch I4. Thus, it may be seen that the direction of communication is under the sole control of the operator at the central station.

The embodiment of the invention illustrated in Fig. 2 differs from that described above in that the remote stations are provided with control means whereby they may select only those messages which they desire to receive from the central station, and the central station is provided with selector means whereby it may communicate with any one or all of the remote stations.

The apparatus at the central station in the modiiication oi' Fig. 2 corresponds identically with that of the previously described embodiment, with the exception of the addition of a selector switch 3i which is placed in the common conductor I3. The selector switch has an arcuate contact 32 adapted in one position to connect the conductor I3 to all the branch conductors I3' leading to the various voice coils 23, and in other positions to engage either one or the other of the branch conductors I3'. In order to4 enable the remote stations to receive only desired messages, each station is provided with a switch 33 normally biased into engagement with a contact 34 connected to the previously described conductor 30 and adapted to be actuated into engagement with a contact 35 connected to the previously described conductor 25. The various contacts 34 and 35 are connected to the conductors 25 and 30 by branch conductors 36 and 31.

In the operation o! the embodiment illustrated in Fig. 2, when the switch Il is in its normal position and the selector switch 3| connecting the common conductor I3 to all the branch conductor-s I3', the system is conditioned for cornmunlcation from the remote stations to the central station by operation of switches 33 into engagement with contacts 35. Upon the described operation of any one of the switches 33, the speaker unit I I, associated therewith. is connected directly across the input of the ampliiier Just as in the previously described modification. In response to a call from any remote station, the` operator at the central station may operate the switch Il to its displaced position, thereby connecting the output or the amplifier to conductor 30. Then, li the operator at the remote station wishes to listen to a communication from the central station, he releases the switch 33. which is then returned into engagement with contact 3l. thus connecting the speaker across the output of the ampliiier. If the operator at any station does not wish to listen to a particular communication i'rom the central station, it is only necessary for him to disengage switch 33 from contact 34 and thereby prevent the transmission of the message to the voice coil of the speaker at that station.

In view of the fact that the central station apparatus is the same as in the modification of Fig. 1, the direction of communication is under the sole control of the operator at the central station. Furthermore, if the operator at the central station desires to communicate with only oneof the remote stations, he may do so by actuating the selector switch 3i to a position in which the common conductor I3 is connected with the branch conductor I3' leading to the particular remote station with which he wishes to communicate.

The embodiment of the invention shown in Fig. 3 diilers from the embodiment shown in Fig. l primarily in the provision of a different type of selector switch at the central station. The selector switch of this embodiment differs from the selector switch in the embodiment of Fig. 2 in that it is so constructed and arranged in the circuit that the operator at the central station may communicate with any one or all of a number of remote stations, exceeding two in num-y ber, and likewise may cut off communication from all remote stations if heso desires. The selector switch 43 consists of a substantially circu'lar contact segment 4| and a contact bar 42 extending centrally from within the segment 4I to a point outside its periphery. The contacts 4I and 42 may be supported in the position illustrated by suitable means, such as an insulating bar n43. The ungrounded sides of the various voice coils 29 are connected to individual contacts adapted to be engaged by the arcuate segment 4I and also by the contact bar 42. When the selector switch ls in the position illustrated, the common conductor I3 is connected to all the branch conductors I3' through the contact bar 42 and a conductor 43 connecting the latter to the arcuate segment 4I, which is in contact with all of the conductors I3. Consequently, with the selector switch in the illustratedposition, any one of the remote stations may communicate with the central station, and the central station likewise may communicate with all the remote stations when the switch I4 is actuated to its displaced position.

Whenever the operator at the central station wishes to communicate with a particular remote station, he actuates switch 4B to connect the contact bar with the conductor I3 leading to the statibn with which he desires to communicate. At this time the common conductor I3 is connected to the desired conductor I3' through the contact bar and the other conductors I3 are disconnected from the common conductor by reason of the fact that the arcuate segment 4I is connected to the common conductor only when the contact bar is in the position illustrated. When the selector switch is actuated in this manner, only the station selected can communicate with the central station and consequently the other remote stations cannot listen to the communication between the central station and the selected remote station.

When the operator wishes to cut off communication with all remote stations, he is able to do so simply by operating switch 40 into a position in which the contact bar 42 is not in engagement with any of the branch conductors I3' or the conductor 43. A

The embodiment of the invention shown in Fig. 4 diiers from that shown in Fig. 3 in the provision oi means for creating a regenerated signal at the central station whenever a switch I3 at the remote station is closed to connect the speaker unit thereat to the input oi the amplifier. The regenerated signal is created by coupling the output of the amplier to the input whenever the switch I5 is closed with the switch I4 at the central station in its normal position. This coupling is provided by means of a circuit extending from the interconnected contacts 20 to conductor 30 and comprising a conductor 45, a current limiting resistance 43, and a switch 41, The switch is biased to its open position, but is adapted to be closed under certain hereinafter described conditions by a cam 43 operatively connected by a shaft 49 for simultaneous operation with the selector switch 43. Ii desired the shaft 49 may be biased to a normal position corresponding to that illustrated in Fig. 4 by a spiral spring 50, so

.that the system is normally `conditioned for calling by the remote stations.

To enable the operator at the central station simultaneously to communicate with all the remote stations, as in the previously `described modications, the selector switch 43 is provided with a stationary contact 44 adapted to be engaged by the contact bar 42 in one position thereof. When the contact bar is in engagement with contact 44 the conductor I3 is connected to all oi the remote stations through the contact bar 42, conductor 43 and contact segment 4I. In this position of the selector switch, the switch 41 is open and consequently the operator at the central station may communicate with all of the remote stations. Likwise, any of the remote stations may communicate with the central station when the selector switch is in this position and the switch I4 is in its normal position.

When the operator at the central station desires to communicate with any particular remote station, he actuates the selector switch 4Il to bring the contact bar 42 into engagement with the particular branch conductor I3 leading to the desired remote station. This operation of the selector switch results in the opening of switch 41, thereby rendering impossible the creation of a regenerated signal in the speaker at the central station. The operator then depresses switch I4 to its displaced position, thereby connecting the voice coil 24 of speaker Ip to the input of the amplier and connecting the output of the amplifier to the remote speakers II. The circuit is, however, completed only through one of these coils, that one being the one associated with the particular branch conductor I3' connected to the conductor I3 by the contact bar 42. The operator at the remote station called may reply when the switch I4 returns to its normal position and the operator closes the switch i5 at the remote station.

If the operator at one of the remote stations desires to call the central station, the selector switch 4I) being in its normal position corresponding to the position illustrated in Fig. 4 and to which it is automatically returned, the operator at the remote station merely closes his switch I5 a predetermined number of times to indicate which station is calling. When he closes this switch a circuit iscompleted between the output and input of the amplifier I2, the circuit extending from the output to the input through conductor I1, switch blade I6, contacts 2|), conductor 45, resistance 46, switch 41 in its closed position, conductor 30, switch I5, conductor 25, switch blade I8. and conductor I3. The result oi this connection is a feed back of energy from the output to the input, and the amplifier regenerates to produce a howl in the speaker ID. The code signal thus emitted by a predetermined sequence of howls informs the operator at the central station that a certain remote station desires to communicate with him. The operatorat the central station thereupon throws the selector switch l to communicate with that particular station and thereby private communication can be maintained in the same manner as in the embodiment shown in Fig. 3. It should be noted that the operators at the other remote stations are unable to cut into the conversation, either to listen thereto or interrupt it.

It is to be noted that while I have shown only a comparatively few stations in each of the embodiments of the invention illustrated, it must be understood that I have no intention to be limited thereto, since the number of remote stations may be multiplied to any extent desired.

Although the invention has been disclosed with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative of the invention, except in so far as set forth in the accompanying claims. l

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A multiple station intercommunication system, including in combination, voice receiving and transmitting means comprising a loudspeaker adapted to function as a microphone and a loudspeaker at each station, an amplifier, a pair of inter-station conductors adapted'selectively to be connected to the input and output of the amplifier, selectively operable means at a first station operable to a first position for connecting the voice receiving and transmitting means thereat to the output and the first conductor to the input of said amplier and to a second position for connecting the voice receiving and transmitting means to the input and the second conductor to the output of said amplifier, and means at another of said stations for connecting the voice receiving and transmitting means thereat to the input of said amplifier through said iirst mentioned conductor and said selectively operable means when the latter connects the voice vreceiving and transmitting means fait the rst station to the output of said ampli- 2. A multiple station communication system, including in combination, a voice receiving and transmitting means comprising a loudspeaker adapted to function as a microphone and a loudspeaker at each station, an amplifier, a pair of interstation conductors adapted selectively to be connected to the input and the output of the amplifier, means at a rst station operable to a first position for connecting the voice receiving and transmitting means thereat to the output and one of said pair of conductors to the input of said amplifier and simultaneously disconnecting the other conductor from said amplifier, and to a second position for connecting the voice receiving and transmitting means to the input and` the said other conductor to the output of the amplifier, and simultaneously ydisconnecting said one conductor from the amplifier, said means including plural position switching means biased to said rst-mentioned position, and means at another of said stations for connecting the voice receiving and transmitting meansthereat to the input of said amplier through said one conductor and said switching means when the latter is in its first-mentioned position.

3. A multiple station communicating system, including in combination, a speaker adapted to 5 function as a microphone and loudspeaker at each station. an amplifier, means at said rst station for selectively connecting the speaker thereat to the output and input of the amplifier, said means including a multi-pole plural-position switch biased to a normal position in which the speaker is connected to the output of the amplii'ler and operable to connect said speaker to the input and the speaker at the second station to the output, and means including a selectively operable switch at the second station for connecting the speaker thereat to the input of said amplier through the first mentioned switch when the latter is in its normal position.

4. An intercommunicating system. including in combination. a central station, a plurality of stations remote therefrom, loudspeaker units adapted to function as microphones and loudspeakers at each station, an amplifier, means including a master switch' at the central station 25 operable into a rst position for connecting the speaker at the central station to the input and the remote speakers directly to the output of the amplifier and operable into a second position for connecting the speaker at the central station to the output and conditioning the remote speakers for connection to the input of the amplifier. means normally biasing said master switch to its second position, and switches at each of said remote stations for completing the connection of the respective speakers to the input of the amplifier.

5. A communicating apparatus comprising a central loudspeaker, a plurality of remotely located loudspeakers adapted to function as microo phones and loudspeakers connected in parallel, a switch associated with each remote loudspeaker, an amplifier, a main switch adjacent the central loudspeaker adapted in one position to connect the central loudspeaker to the input of the amplifier and the other loudspeakers directly to the output of the amplier, and in another position to connect the central loudspeaker to the output and the remote switches to the input, and means normally holding the main switch in said last position whereby each remote speaker may be connected by its switch at will to the input of the amplifier when the main switch is in its normal position.

6. A communicating apparatus comprising a pair of remotely located loudspeakers adapted to function as microphones and loudspeakers, an amplifier, a multi-pole plural-position switch `adjacent one speaker having one of its poles cons nected to theinput of the amplifier and another pole connected to the output of the amplifier. means normally holding said switch in one posi-A tion, contact means adapted to be engaged by the last mentioned pole in the normal position of the switch and by theflrst mentioned pole in 05 the actuated position of the switch, a conductor connecting said contact means to the adjacent loudspeaker, contact means engaged by the first mentioned pole in the "normal position of the switch, a conductor extending from the last mentioned contact means to the remote speaker, a switch for connecting said last mentioned con'- ductor to the remote speaker, contact means engaged by the second mentioned pole when displaced from normal position, and a conductor aieases connecting said last mentioned contact means directly to the remote speake 7. An intercommunicating system, including in combination, a central station, a remote station, loudspeaker units adapted to function as microphones and loudspeakers at eachistation, an amplifier, a pair of interstation conductors adapted selectively to be connected to the amplifier means including a master switch at the central station operable into a first position for connecting the speaker thereat to the output and conditioning the other speaker for connection to the input of the amplifier by connection of a first interstation conductor to the input of the amplifier and operable into a second position for connecting the speaker thereat to the input and conditioning the other speaker for connection to the output of the amplifier by connection of a second interstation conductor to the output of the amplifier, a switch at the remote station operable into a first position to complete the connection of the speaker thereat to the output through said second interstation conductor and a second position to complete the connection of the speaker to the input of the amplifier through said first interstation conductor, and means biasing both of said switches to their first positions whereby the system is conditioned for initiation of communication from either station by operation of the switch thereat to its second position.

8. `An intercommunicating system including in combination, a central station, a plurality of remote stations, loudspeaker units adapted to function as microphones and loudspeakers at each station, an amplifier, a pair of interstation conductors adapted selectively to be connected to the amplii'ier means including a master switch at the central station operable into a first position for connecting the speaker unit thereat to the output and conditioning the remote speakers for connection to the input of the amplifier by connection of a first interstation conductor to the input of the amplifier, and operable into a second position for connecting the speaker thereat to the input and conditioning the remote speakers for connection to the output of the ampliiier by connection of the second interstation conductor to the output of the amplifier, a switch at each remote station operable into a first position to complete the connection of the speaker thereat to the output through said second interstation conductor and to a second position to complete the connection of the speaker thereat to the input of the amplifier through said first interstation conductor, means biasing the master and all the remote switches to their first mentioned positions whereby the system is conditioned forlnitiation of communication from any station by operation of the switch thereat to its second position. f

9. A multiple station intercommunlcating system, including in combination, loudspeaker units adapted to function as microphones and loudspeakers at each station, an amplifier, control means at one of said stations for connecting the speaker thereat to the output of the amplifier and for conditioning the station for connection to the input of the amplifier, control means at the second station operable to complete the connection of the speaker thereat to the input of the amplifier, and means for creating an audible signal at the first station rendered effective upon operation of said last mentioned means to complete the connection.

l0. A multiple station intercommunicating system. including in combination, loudspeaker units speaker at a second i speakers at each station.

adapted to function as microphones and loudan ampliiier, control means at a central station normally connecting the speaker thereat to the output of the amplifier and conditioning the remaining speakers for con-yk nection to the input of the amplifier, control means at each of said remaining stations operable to complete the connection of the speaker thereat to the input of the amplifier, and means for creating a regenerated signal in the speaker at` the central station rendered effective upon operation of any of said last mentioned control means to complete said connection.

ll. A multiple station intercommunicating systern, including in combination, loudspeaker units adapted to function as microphones and loudspeakers at each station, an ampliiier, control means at a central station adapted to connect the speaker thereat to the output of the amplifier and condition the remaining speakers for connection to the input of the amplifier, control means at each of said remaining stations operable to complete the connection of the speakers thereat to the input of the amplifier, means for creating an audible signal in the speaker at the central station upon operation of any of said last mentioned control means to complete said connection, and other control means at the central station for rendering said last mentioned means inoperative.

l2. A multiple station intercommunicating system, including in combination, loudspeaker units adapted to function as microphones and loudspeakers at each station, an amplifier, control means at a central station normally connecting the speaker thereat to the output of the amplifier and conditioning the remaining speakers for connection to the input of the lamplifier, control means at each of said remaining stations operable to complete the connection of the speakers thereat to the input of the amplifier, means for creating an audible signal in the speaker at the central 'station upon operation of any of said last mentioned control means to complete said connection, selector means at the central station normally connecting all said remaining stations to said central station and operable to connect any one of said remaining stations to said central station, and means operable simultaneously with 'a normal position to connect the speaker thereat to the output of the amplifier and operable to connect said speaker to the input and condition the remote speaker for connection to the output, means including a normally open switch at the remote station for connecting the speaker thereat to the input of the amplifier through the first mentioned switch when the latter is in its normal position, and means including a circuit comprising a resistance element and switch at the central station for connecting the output to the input to produce a regenerated signal in the speaker at the central station whenever the switch at the remote station is operated to connect the speaker thereat to the input,

14. A communicating apparatus comprising a pair of remotely located loudspeakers adapted to function as microphones and loudspeakers, an amplifier, a double pole double throw switch adjacent one speaker having one of its switch blades connected to the input of the amplifier and the other switch blade connected to the output of the amplifier, means normally holding the switch in one position, contact means adapted to be engaged by the second mentioned switch blade in the normal position of the switch and by the first mentioned switch blade in the actuated position of the switch, a conductor connecting said contact means to the adjacent loudspeaker, contact means engaged by the second mentioned switch blade when displaced from normal position, a conductor connecting said last mentioned contact means to the remote speaker, a circuit including a current limiting resistor and a switch located near the main speaker whereby said first mentioned contact means may be connected to the second mentioned contact means, contact means engaged by the first mentioned switch blade in the normal position of the switch, a conductor extending from the last said contact means to the remote speaker, and a switch for connecting the last mentioned conductor to the speaker.

15. A multiple station communicating system, including in combination, voice receiving and transmitting means comprising a loudspeaker adapted to function as a microphone and a loudspeaker at each station, an amplifier, selectively operable means at a first station for connecting the voice receiving and transmitting means thereat to the output and input of said amplifier, means at the remaining stations for connecting the voice receiving and transmitting means thereat to the input of said amplifier through said selectively operable means when the latter is operated to connect the voice receiving and transmitting means at the first station to the output of said amplifier, and single control means at the rst station for selectively controlling the connection of the speakers at the remaining stations to the amplifier, whereby the iirst station can communicate with any or all the remaining stations.

16. A multiple station communication system, including in combination,` loudspeaker units adapted to function as microphones and loudspeakers at each station, an amplifier at a rst station, selectively operable means at said first station for connecting the speaker thereat to the output and input of said amplifier, control means at each of the remaining stations operable to connect the speakers thereat to the input of said amplifier through the selectively operable means when the latter is operated to connect the speaker at the first station to the output of the amplifier, means including a switch at the first station operable to a position wherein it cooperates with the selectively operable means and control means to connect the output to the input of the amplifier for producing by regeneration an audible signal in the speaker at the first station, and a selector switch mechanically connected for simultaneous operation with the last mentioned switch, said selector switch being operable to two positions in which all the said remaining speakers are connected to the amplifier and in one of which positions the switch mechanically connected thereto is in circuit making position, whereby the control means at remaining stations may be operated to produce a regenerative signal at the first station, and in the other of which positions the said switch is in circuit breaking position, whereby the first station may call simultaneously all the remaining stations, said switch being operable to other positions to connect any` one of said remaining speakers to the amplifier to the exclusion of the others, at which positions the switch mechanically connected thereto is in circuit breaking position.

1'7. In an inter-communicating system, the combination including a plurality of stations, voice receiving and transmitting means comprising a loudspeaker adapted to function as a microphone and a loudspeaker at each station, an amplifier, a circuit comprising two inter-station conductors connecting the voice receiving and transmitting means at the stations, control means at a first station for selectively connecting the voice receiving and transmitting means thereat to said conductors through said amplifier, control means at the remaining stations for connecting the voice receiving and transmitting means thereat to said conductors, said conductors and control means being so arranged that only one of said conductors is connected to the amplifier when communication is established in either direction.

18. A multiple station inter-communicating system including, in combination, voice receiving and transmitting means at each station, an ampliiier, selectively operable means at a iirst station for connecting the voice receiving and transmitting means thereat to said amplifier, selectively operable means at the remaining stations for connecting the voice receiving and transmitting means thereat to the amplifier, and means rendered effective upon operation of the last mentioned means into a predetermined position to couple the output to the input of the amplifier for creating an audible signal at the first station.

19. In an inter-communicating system of the type including a central station and a plurality of remote stations, the combination including voice receiving and transmitting means at each station, a communication direction control switch at the central station, and a single selector switch at the central station so constructed and arranged with respect to the remote stations that communication may be established between the central station and any one or all the remote stations.

20. A multiple station inter-communicating system comprising a loudspeaker adapted to function as a microphone and a loudspeaker including, in combination, voice receiving and transmitting means at each station, an amplifier, selectively operable means at a first station for connecting the voice receiving and transmitting means thereat to the amplifier, selectively operable means at the remaining stations for connecting the Voice receiving and transmitting means thereat to the amplifier, and a rotary selector switch at the first station so constructed and arranged with respect to the said remaining stations that any one or all of the remaining stations may be connected to said amplifier.

21. In combination, voice receiving and transmitting means of the type adapted to function both as a microphone and a loudspeaker, an amplifier, a communication circuit comprising two conductors, and control means for said voice receiving and transmitting means, amplifier and conductors, said control means being so constructed and arranged that it can be manipulated to connect said voice receiving and transmitting means to the input and one of said conductors to the output of the amplifier or to connect said voice receiving and transmitting means to the controlling the connections of the amplifier, voice receiving and transmitting means and communication circuit, and a selector switch located in the common return circuit so constructed and arranged with respect to the various stations that communication may be established between a station at which the selector switch is located and selected stations remote therefrom.

R. H. CAMPBELL.

CERTIFICAm 0F CORRECTION.

Patent No.l 2,162,568.

RICHARD H.

` June 15, 1959. CAMPBELL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, second column, lines 50 and 51, claim 20, strike out the words "comprising a loudspeaker. adapted to function as a microphone anda loudspeaker" and insert the same after "means" in line 55, same claim; and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of Sentember, A. D. 1959.

(Seal) Henry Van Arsdale,

Acting Commissioner of Patents.

controlling the connections of the amplifier, voice receiving and transmitting means and communication circuit, and a selector switch located in the common return circuit so constructed and arranged with respect to the various stations that communication may be established between a station at which the selector switch is located and selected stations remote therefrom.

R. H. CAMPBELL.

CERTIFICAm 0F CORRECTION.

Patent No.l 2,162,568.

RICHARD H.

` June 15, 1959. CAMPBELL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, second column, lines 50 and 51, claim 20, strike out the words "comprising a loudspeaker. adapted to function as a microphone anda loudspeaker" and insert the same after "means" in line 55, same claim; and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of Sentember, A. D. 1959.

(Seal) Henry Van Arsdale,

Acting Commissioner of Patents. 

